This invention relates to methods and apparatus for the elimination of dissolved air from ink used in an ink jet apparatus and, more particularly, to a new and improved method and apparatus for deaerating ink in a highly effective manner.
In many ink jet systems, ink is supplied to a chamber or passage connected to an orifice from which the ink is ejected drop-by-drop as a result of successive cycles of decreased and increased pressure applied to the ink in the passage, usually by a piezoelectric crystal having a pressure-generating surface communicating with the passage. If the ink introduced into the passage contains dissolved air, decompression of the ink during the reduced pressure portions of the pressure cycle may cause the dissolved air to form small bubbles in the ink within the passage. Repeated decompression of the ink in the chamber causes these bubbles to grow and such bubbles can produce malfunctions of the ink jet apparatus.
Heretofore, it has been proposed to supply deaerated ink to an ink jet apparatus and maintain the ink in a deaerated condition by keeping the entire supply system hermetically sealed using, for example, flexible plastic bags or pouches as a deaerated ink supply. Such arrangements are not entirely satisfactory, however, because the flexible plastic pouches are at least partially air-permeable and, in hot melt ink systems, this problem is aggravated because the plastic pouch material becomes more permeable to air at elevated temperatures at which the heated ink is capable of dissolving large amounts of air, e.g., up to 20 percent by volume. Moreover, air may dissolve into the ink at the ink jet orifice during periods of non-jetting. Such dissolved air may diffuse through the ink into the jet pressure chamber, and thereby cause malfunction of the jet. Consequently, air bubble formation in the ink jet head of a hot melt jet apparatus is a primary cause of hot melt ink jet failure.
Accordingly, it is an object of the present invention to provide a new and improved method and apparatus for eliminating dissolved air from ink in an ink jet system which overcomes the above-mentioned disadvantages of the prior art.
Another object of the invention is to provide a system for deaerating ink in an ink jet system and for purging any air bubbles which have been formed in the ink jet head.